The invention relates to a method for drying sludge, in particular sewage sludge, which produces granulate from the dried product. According to said method, a mixture of a carrier material, consisting of recycled sludge that has already been dried, and wet sludge is fed to a dryer. The invention also relates to an installation for carrying out said method.
Drum drying plants have been known for a number of years. This type of installation and method is described specifically for drying sludge, in particular sewage sludge, in e.g. EP 0 789 209 or U.S. Pat. No. 5,318,184. What these installations have in common is that they provide for carrier material, consisting of material that has already been dried, being mixed back into the liquid sludge in order to eliminate the so-called sticky phase. In order to do this, a large portion of the material that has already been dried is brought to a carrier material silo by a number of conveying elements. From here, it is added to the liquid sludge according to various controlling variables and after being mixed into it, fed to the dryer again. In order to be able to store the dried material in the silo, it has to be cooled using a special cooling device (e.g. a cooling screw). In addition, the silo for the carrier material must be of a special, expensive design for safety reasons.